Synthesis of aromatic hydrocarbons



"2,815,357 SYNTHESIS OF AROMATIC HYDROCARBONS Herman S. fieelig, Valparaiso, andHerman I. Weck, Dyer, Ind assignors to Standard Oil Company, Chicago, 11]., a corporation of Indiana No Drawing. ApplicationiMarcll 12, 1954, Serial No. 415,956

7 Claims. :(Cl; 260-449 This invention relates to a process for thesynthesis of hydrocarbons, particularly aromatic hydrocarbons, from :mixtures of carbon monoxide --with hydrogen in thepresence of catalysts.

In the well-knownFischer-Tropsch synthesis, iron-type or alkali-promoted thoria catalysts havebeen-employed to produce parafiins and olefins,--accompanied by-very minor proportions,-at most, of aromatic hydrocarbons and by variable yields of oxygenated --organic "compounds, depending upon the particular catalyst'and synthesis conditions. The octane rating of conventional Fischer-Tropsch synthesis products is .low and it has heretofore been necessary to reform the synthesis products in order to increase the octane value thereofttoia suitable range for use in internal combustion engines.

It is an object of this invention to provide a catalytic synthesis process which can be operated to produce subtantial yields of liquid hydrocarbonsboiling substantially within the gasoline boiling range --and'comprising -preratios betweenrabout -1/4..and 4/1; at. temperatures betweenfabout 6'00. and about 850 F. and pressures of at least about400.p.-.s. i.'g. up to.about.=l0,000.:p.zs. iz. gzzor even higher, ,e. ;.g.l25,"000, ,p. s. i. g.,,at space velocities (volume "of 'gas per -hourperm volume ofz'catalyst) :of .:at least about 50.up.to..'about 5000 (in-,fixed-bed' reactors) or even much higheryfor example up:to=about 20,000. (in

fluidized-bed reactors). The; preferred. temperature .range is about 650 to*about-800*Fa-and the-preferredqpressnre range is about 450 "toz'about 5000 ip..;s.. i. g. EPreferred operating conditions can be determined in specific instances by small scale tests in-Which operating; variables are systematically explored.

2,815,35 7 :Patented. Dec. 3, 1.957

The catalysts employed in .the practice of the present invention comprise essentially zinc oxide or zinc sulfide supported upon an activated alumina (a,gamma alumina) containing less than about 0.3, w. percent (preferably less than 0.1'w. .percent)-of alkali metal (calculated as alkali'metal oxide) and containing anacid-acting fluoride asapromoter. Theproportion of acid-acting, fluoride, 'calculated'as HF, inthe catalyst .can..,be varied between about 0.1 and about 2.5 w. percent, but is preferably present within the .catalyst in proportionsbetween about 0.2 andabout 1.0 W. percent. .As will appear" hereinafter, the proportion of 'zinc, oxide or. sulfide in .the catalyst must be closely controlled in order tosecure the best tyields'of aromatic'hydrocarbons inthe synthesis. 'The proportion of zinc oxide .or sulfide in the 'finishedcatalyst can beivaried between about 1 and about 20 w. percent, and-istpreferably between about 2 and about 10w, .percent. .In lieu of the alumina supporter in. partial replacement thereof, we may employ. other diificulty re- "ducible -metal oxides .selectedfrom the class. of titania, zirconia and vanadia.

Althoughzinc oxide-alumina catalysts have heretofore "been employed for the reduction of carbon monoxide .to "produce hydrocarbons, the yields. of aromatic hydrocarbons have heretofore been .nil or lowfor two reasons "not appreciated by prior art investigators:

(1)1Alumina, as ordinarily prepared .bythe precipita- "tion of aluminum nitrate with sodium carbonate'followed by. repeated washings with waterand drying, contains .of "the order of 1.5 w. percent of Na O. .Althouglr alkali 'metal" oxides are desirable promoters 'for;iron-type synthesis 'catalysts,even relatively small proportions of. alkali metal oxides serveto prevent theformation of. aromatic hydrocarbons when present inzinc oxide-alumina catalysts.

(2)Acid-acting fluorides are 'remarkable'promoters 'forzinc' oxide-alumina catalysts in that they inducea 'very' large increase in the yield of aromatic hydrocarbons in the synthesis process while inducing only a relatively minorincreasejin the extent of carbon monoxide. conversion.

,As 'a consequence of the presenthinvention new sources ofindustrially attractive aromatichydrocarbons become available.

'"The-zincoxide-alumina and zinc sulfide-alumina catalysts'havingan alkali metal oxide contentbelow about 0.3 "w. percent can beprepared by known methods or com- 'binations of known methods. Aparticularlydesirable method of making an activatedalumina containinglittle or=no"alkali'metal oxide involves the preparation'of an alumina sol-by'the reaction of aluminum amalgam -with -a-*dilute aqueoussolution of an organic acidsuch as formic'acid oracetic acid, which sol is then treated with ammonium hydroxide to precipitate asuper-pure alumina g'el-containinglittle or'no alkali metal oxide;-this is the so-called Indiana alumina sol-technique. References 'to the preparation of super-pure alumina solsare given "inour I copending application Serial. 1 No. 325,"7-78,-filed December 13, '1952, -now -U. .S. "Patenf 2,727,0 5 5 ln order to prepare a zinc oxide-alumina catalyst, zinc nitrate is added to the alumina sol before precipitation. The acid-acting fluoride may also be incorporated with the zinc nitrate and the alumina sol, in proportions desirable to effectively promote the synthesis action of the finished catalyst.

Thus a suitable catalyst may be prepared by mixing an aqueous solution containing the desired proportions of zinc nitrate or other water-soluble zinc salt, ammonium fluoride and Indiana alumina sol, precipitating oxides of zinc and aluminum containing fluoride by the addition of ammonium hydroxide solution, filtering the precipitate, thereafter slowly drying the precipitate in air at a suitable temperature (for example, about 185 F.) and finally calcining the catalyst in air, for example at a temperature of about 900 F. It will be understood that the alumina component of the catalyst maybe partially or completely replaced by titania, zirconia or vanadia of suitably low alkali content. The ZnSAl O -fluoride catalyst can be prepared by similar methods.

The acid-acting fluorides employed to promote the catalysts are HP or materials capable of forming hydrogen fluoride by thermal or hydrolytic decomposition at or below the temperatures employed in the synthesis operation, e. g. ammonium fluoride. Since the catalysts inevitably contain water as prepared (usually about 1 to w. percent water), they may be treated with materials which are capable of reacting with water to produce hydrogen fluoride. Such materials include fluorine, ClF BrF BF carbonyl fluoride, acyl fluorides and reactive alkyl fluorides, although the latter may be used as sources of I-IF via thermal decomposition. Examples of acyl fluorides include acetyl fluoride, propionyl fluoride, hexahydrobenzoyl fluoride, etc. Suitable alkyl fluorides include ethyl fluoride, isopropyl fluoride, sec-butyl fluoride, etc. In lieu of or in addition to ammonium fluoride, we may employ various hydrofluorides of volatile amines, such as methylammonium fluoride, trimethylammonium fluoride, triethylammonium fluoride, etc. The incorporation of acid-acting fluoride may be achieved through treatment of the refractory metal oxide catalyst support (alumina or the like) prior to the incorporation of the zinc oxide or zinc sulfide component; by treatment of the zinc oxide or zinc sulfide component of the catalyst; by treatment of the catalyst prior to or after drying or calcining; by the introduction of acid-acting fluoride into the reactor during synthesis, for example, by the inclusion of very small proportions of certain of the acid-acting fluorides intermittently in proportions sufficient to activate the catalyst and to affect its selectivity for the synthesis of aromatic hydrocarbons.

In order more specifically to describe and illustrate the invention, without the intent unduly to limit the same, illustrative examples are provided hereinafter. The zinc oxide-alumina catalysts employed in the examples were prepared by coprecipitation of zinc oxide and alumina (derived from an Indiana sol) by the addition of aqueous ammonia to a mixture of zinc nitrate and Indiana alumina sol and activated by the addition of a suitable proportion of HF or ammonium fluoride before the coprecipitation of the metal oxides. These catalysts were characterized by their low content of alkali metal oxide, viz. below about 0.1 w. percent. In all instances the synthesis gas contained 50 mol percent each of hydrogen and carbon monoxide. One hundred thirty ml. of catalyst was contained in a copper tube inserted within a vertical stainless steel reactor. The synthesis gas was passed downwardly through the fixed bed of catalyst, thence in sequence through three product separators operated, respectively, at

'300 F., 80F. and 32 F. A convenient and suitable space velocity was chosen in the examples, viz. about 500 volumes of gas per hour per volume of catalyst.

The following data afford a direct comparison of the effects of promoting a zinc oxide-alumina catalyst with an acid-acting fluoride, compared with an unpromoted catalyst. The test runs recorded in Tables 1 and 2 were performed at 450 p. s. i. g.

TABLE 1 Z710 on Al203 Product carbon distribution Yields (grams/ (Percent 0) normal cubic Percent meter) Temp., F. 00

conv.

Ca-I- 03+ Arom. 002 01-0: (non- Arom. (total) only arom.)

( 0.01% Nero by emission spectrographic analysis.

TABLE 2 10% ZnO on A1 0 Promoted with 1% NH F Product carbon distribution Yields (grarns/ (Percent 0) normal cubic Percent meter) Temp, F. 00

conv.

Cu+ 03+ Arom. CO: C1-C2 (non- Arom. (total) only arom.)

Volume percent Paraflins and naphthenes 4.

Olefins 2.5 Aromatics 93.0

The liquid products were then fractionally distilled and subjected to infrared absorption analysis with the following results:

TABLE 3 Boiling Refractive Vol. range, index range percent Constituent 112-135. 1. 410-1. 450 3. 6 Peraflins and oleflns of the type C=CH and C=CH1 (R is alkyl) and 10% toluene.

-150-..- 1. 450-1. 476 3. 4 Metaand parnxylene.

-193 1. 465-1. 502 15.4 1,2,3- and 1,2.4-trimethylbcnzenc; 1-

rnethyl-2-ethyl-, 1-methyl-3cthyl-, and l-mcthyl-4-ethylbenzene.

193-203- 1. 502-1. 508 5. 7 1,3-dlmethyl-3ethylbenzene; 1,3- and 1.4-dimethyl-2-ethylbenzenc.

203-205." 1.508-1. 510 3. 6 Durene and isodurene.

205-232.. 1. 508-1. 510 15. 5 1,2,3.4-tetramethylbenzene and other unidentified aromatics.

232-234. Solid 3.4 Pentamnthylbenzene.

234-258- 1.519 15.8 Z-methylnaphthalene and other unidentified aromatics.

258-282- Solid 8. 0 Hcxamethylben zene.

282-302-- 1. 529-1. 591 15. 2 Unidentified aromatics.

302-328.-- Solid 1. 7 Possibly 1-phenylnaphthalene.

328+- Solid 8. 7 Residue.

asters? Further examples of our invention are: illustrated. inthe following tabulation of data:

TABLE 4 Fluoride-promoted 2110 on A1 catalysts [1/1 Hz/CO synthesis gas used in all runs at a space velocity at 500v./v./hr.]

Run No P40 L-43 K-47 K-4s L46 1 41 L-44 X-5 Percent ZnO 3 10 10 10 10 10 Percent NHiF 1 0.5 4 1 0.5 Percent HF 0.5 Percent KF... 0.8 Percent K200 0. 5 Percent N890... 0.08 0.02 0.03 0. 02 0.08 0.05 0. 02 0. 02

Aromatic yields, g/n. cu. m. H;+CO consumed Percent 00 conversion.

0. 5' 0.0 12 a s s 5 16 12 7 10 12 12 1a 11 13 19 24 23: 16 14 10' 10 1s 12 11 a R. I. ofproductoll (11. at 800 F 1.5218 1.5297 1.5129 1.5122 1.5205 1. 5143 1.5327 1.5149

By emission speetrographic analysis.

The above table illustrates the results obtainable by variresulting suspension with a suitable proportion of Indiana ation in the proportion of zinc oxide in the catalyst. A alumina sol, followed by the precipitation of a gel by the comparison of runs P-40 and L-43 with K-48 shows addition of an aqueous ammonia solution in the proporthat catalysts containing 3 to 10 weight percent Z110 gave tion required to adjust the pH of the mixture to 8. The good results and are somewhat preferable to the 20% resulting gel was dried in air at approximately 185 F. ZnO catalyst of run K-48. These runs also illustrate reand then was dried and treated with air at 900 F. for 4 sults obtainable by variation of the proportion of ammoni- 50 hours. um fluoride in the catalyst from 0.5 to 4%. In run L-46, TABLE 5 HF is shown to be the substantial equivalent of ammom- Experimental results from run um fluoride as a promoter in the synthesis. In run R41 0 1 n 0 w 9 the use of KF as a promoter is illustrated. Run L-44 ill m gfi fi f f lustrates the use of a high alkali content ZnO--A1 O 5 catalyst which is not promoted with a fluoride. A com- Run period A B C D E F parison of this run with the run of Table 1, wherein a lowalkali unpromoted ZnOAl O catalyst was used, shows Hours n 72 72 72 72 72 4% the marked inhibiting effect of alkali on the yields of arog s- 0 Re 70( 35g 20g 35g 30g 37g matic hydrocarbons which are obtainable in the synthes s .3.3 3. ggg g 3 at temperatures between about 700 F. and about 800 Prodlclct v g i gra sl F. and also shows that the maximum yield of aromatic hy- 5. 5 2 drocarbons with the low-alkali unpromoted catalyst is very 1 -7 55.0 51-6 48-2 27.6 7.3 Aromatfc 31.7 45.1 42.3 39.5 22.6 6.0 much hlghel "than With the high-311K311 Impromoted R. I. of oil ii a ctiou .5000 1.4999 1.4993 1. 4840 1.4891 1.5127 lyst, Furthermore, a cgmparison of the data 0f Table 1 R. I. of water fi'actio .3365 1.3360 1.3350 1.33 11 1.3338 1.3331 and run L-44 with the other runs, in which fluoride-pro- 1 Based on a 1007 weight balance on an output basis. g t 2 ifi i 1 d ff i gii h 2 Based on arbon balance on an output basis.

a muc igeruimaeyie so aomic T bons are obtainable with the latter catalysts. proper se1ect.l0n and activation of catalysts for i purposes of aromatics production from carbon monoxide Run X-5, which was carried out at 900 p. s. i. g., shows 7 a clear and marked advantage from the standpoint of arofi hydrogen 15 at Purely f Procedure matic hydrocarbon yields over the other runs in Table 4, 511165 1116112061 if predigtmg the suitability of catsalysts hi h were ff t d at 450 i gor promoters or t e state purpose is now own. cem- The following data were obtained by the employment ingly similar catalysts from the standpoint of chemical of a fluoride promoted ZnS-Al O catalyst. The cata- 75 constitution, show widely different capacities for producing aromatic hydrocarbons in the synthesis reaction, as will be evident from the data of Table 6 below:

TABLE 6 Examples of other catalysts tested for the synthesis of aromatics Percent Aromatic Catalyst yield,

conversion g./n.

cu. m.

ZnO 25 3 ThO2+0.1% K200; (K2003 precipitated) 21 11 9% Ti02 on A1203 7 11 8% ZrOa on A1203 13 7 ThOz+5.0% K200i (K2003 precipitated). 26 W03 on A1103. 17 2 10% 00203 on A1203 1 10% ThOz-|l% KzCOa on A1201. 1O Trace 5% Moss on A1101.-- 63 None 8% M00: 0n A110: 50 None 0.0% Pt on A1109 48 None V2 48 None 1.0% ZrSz on ZrOz- 40 None 10% W03 on ZlOz 40 None 10% MoOi+l.0% NHiF on A1203. 22 None '7 AgzO on A1203 10 None 10% Nla+O.5% NHiF on A120 ll None 9% Snort-0.5% NHiF on A1201- 14 None 8% MnOs on A1203 9 None 9% Shot on A1203--- 9 None 9% B203 011 AlzO3.. 2 None 90% SiOz-10% A1203 0 None The above results represent the best yields which could be obtained in operations at 500 space velocity, equimolar proportions of hydrogen and carbon monoxide in the feed, a fixed bed of catalyst, and temperatures within the range of 700 F. to 975 F. The low aromatics productivity of ZnO alone will be apparent from the above table. It

will be noted that ZnO alone showed scarcely any capacity for aromatics synthesis.

It will be understood that the conventional means of synthesis catalyst regeneration can be employed to reactivate partially spent fluoride-promoted Zinc oxide-alumina catalyst.

The partially spent synthesis catalyst may be regenerated by burning carbonaceous deposits contained therein with a gas stream of low oxygen content at a maximum temperature not exceeding about 1000 to 1200 F. and fortification of the catalyst with fluoride promoter. Zinc sulfide catalysts may be sulfided by treatment with hydrogen sulfide or otherwise before being re-used in synthesis.

Conventional synthesis reactors of either the fixed-bed or fluidized-bed type may be employed in practicing the process of the present invention. It will be understood that unconverted gases may be recycled to the reactor or passed to a secondary reactor containing the promoted catalyst.

The aromatic hydrocarbon products of the present invention are practically uncontaminated with paraflins or olefins. The gasoline boiling range fractions may be employed alone or as blending components in motor gasoline or aviation fuels. The aromatic product mixtures produced by the process of this invention can be subjected to known separation procedures to produce concentrates of individual aromatic hydrocarbons or mixtures of isomers, which may be of value for the purpose of producing chemical derivatives.

Having thus described our invention, we claim:

1. A process for the preparation of hydrocarbons, including a substantial proportion of aromatic hydrocarbons, which process comprises contacting a mixture of hydrogen and carbon monoxide in a volume ratio between about 1:4 to 4:1 with a catalyst comprising essentially about 1 to about 20 weight percent of a compound of zinc selected from the class consisting of zinc oxide and zinc sulfide supported upon a difficultly reducible metal oxide selected from the class consisting of activated alumina, titania, zirconia and vanadia, between about 0.1 and about 2.5 weight percent of an acid-acting fluoride, calculated as HF, and not more than about 0.16 weight percent of alkali metal, calculated as oxide, effecting said contacting at a temperature between about 600 F. and about 850 F. at a pressure of at least about 400 p. s. i. g., and separating synthesis products including a substantial proportion of aromatic hydrocarbons.

2. The process of claim 1 wherein said difficultly reducible metal oxide is an activated alumina.

3. The process of claim 1 wherein said compound of zinc is zinc oxide.

4. The process of claim 1 wherein said compound of zinc is zinc sulfide.

5. The process of claim 1 wherein the catalyst consists essentially between about'2 and about 10 weight percent zinc oxide supported upon activated alumina, said catalyst contains between about 0.2 and about 1.0 weight percent of an acid-acting fluoride, calculated as HF, said catalyst contains not more than about 0.1 weight percent of an alkali metal, calculated as oxide, and said contacting is effected at a temperature between about 650 F. and about 800 F. at a pressure of at least about 400 p. s. 1. g.

6. The process of claim 5 wherein said acid-acting fluoride is hydrogen fluoride.

7. The process of claim 5 wherein said acid-acting fluoride is ammonium fluoride.

References Cited in the file of this patent UNITED STATES PATENTS 2,194,186 Pier et a1 Mar. 19, 1940 2,500,146 Fleck et al Mar. 14, 1950 2,727,055 Seelig et al Dec. 13, 1955 

